Ultra wide bandwidth (UWB) systems have recently received considerable attention for wireless radio communication systems. The Federal Communications Commission (FCC) has allowed UWB systems for limited indoor and outdoor applications in the U.S.A., Federal Communications Commission, “First report and order 02-48,” February 2002.
As one advantage, UWB can transmit data at a high rate over a short range. This makes UWB a promising candidate for personal area networks (PAN) in general, and home networks in particular. Recognizing this potential, the IEEE has formed the 802.15.3a standardization group, whose task is to establish a physical-layer standard for UWB communications with data rates over 100 Mbit/s, R. Roberts (Ed.), IEEE P802.15 Alternate PHY Call For Proposals, Document IEEE P802.15-02/372r8, 2002.
The IEEE 802.15.3a standardization group has defined performance requirements for the use of UWB in short range indoor communication system. Throughput of at least 110 Mbps at 10 meters are required. This means that the transmission data rate must be greater. Furthermore, a bit rate of at least 200 Mbps is required at four meters. Scalability to rates in excess of 480 Mbps is desirable, even when the rates can only be achieved at smaller ranges.
A number of possible modulation/multiple access schemes are considered for a physical layer of an ultra wide bandwidth (UWB) communications system by the IEEE 802.15.3a standards working group. One scheme is multiband orthogonal frequency division multiplexing (OFDM) combined with time-frequency interleaving, A. Batra et al., “Multiband-OFDM physical layer proposal”, IEEE P802.15-03/268r2, November 2003. It should be noted that the 802.15.3a time-frequency interleaved OFDM scheme has important differences from conventional OFDM as used, e.g., in asynchronized digital subscribe line (ADSL) and IEEE 802.11a wireless LANs.
In practice, OFDM signals are not demodulated by multiple parallel local oscillators for down conversion in an OFDM receiver. Rather, a fast Fourier transform (FFT) of the received signal is equivalent to the signal received on the individual tones. In a practical implementation, the FFT operates on a block of samples of the received signal, e.g., see May et al., “Orthogonal Frequency Division Multiplexing,” Part IV, Molisch (Ed.), Wideband Wireless Digital Communications, Prentice-Hall, pp. 309-385, 2001. The FFT is typically implemented as a ‘butterfly’ structure, see, van Nee et al., “OFDM for Wireless Multimedia Communications,” Artech House, pp. 46-51, January 2000.
It is desired to improve interference suppression for such a modulation scheme because interference suppression can improve the overall performance of the system.